Coordination Asymmetry Stabilizes a Low-Iridium Cobalt Spinel Oxide Anode for Durable Proton-Exchange Membrane Water Electrolysis

Low-iridium cobalt spinel oxides are promising anode catalysts for proton-exchange membrane water electrolyzers (PEMWEs), but their practical application remains limited by the structural instability of Ir–O–Co motifs at high current densities. Here, we show that the simultaneous incorporation of Mn and Ir into the octahedral (O h ) sites of Co 3 O 4 to form Ir 0.1 Co 1.93 Mn 0.97 O 4 markedly enhances both acidic oxygen evolution activity and durability. In contrast to the single-doped analogues, in which Mn is predominantly stabilized as Jahn–Teller-active Mn 3+ in Co 2 MnO 4 and Ir exists as less oxidized Ir >4+ in Ir 0.1 Co 2.9 O 4, Ir 0.1 Co 1.93 Mn 0.97 O 4 exhibits an optimized local coordination environment with Jahn–Teller-suppressed Mn 4+ and high-valence Ir >4+ species at the O h sites. This distinctive local coordination chemistry enhances structural robustness while promoting catalytic activity under operating conditions. In a practical PEMWE, Ir 0.1 Co 1.93 Mn 0.97 O 4 sustains stable operation for 2800 h at 0.5–1.0 A cm –2, outperforming most reported low-Ir-loading catalysts. This work highlights the importance of coordination asymmetry in the design of durable electrocatalysts for clean energy conversion.